John of St. Thomas, Cajetan, Suarez, Billot, Billuart, Torquemada, Vittoria, and many other fine theologians opined that a heretic remains pope until such time as the Church declares God has deposed him.
Against these, the sedevacantists hold to a contested interpretation of St. Bellarmine.
Fine and well.
But let’s not pretend the R&R position is irrational or untenable, when theologians as great as those mentioned above held the same position.